The attenuated phenotype of tissue culture adapted strains makes HAV an ideal virus to develop as an expression vector. Several different constructs using the infectious cDNA of HAV as the backbone have been made. In HAVvec1, we inserted a multiple cloning site and the cleavage site for 3Cpro just prior to the viral polyprotein initiation site into the infectious cDNA of HAV and showed that this construct was infectious. We inserted synthetic oligonucleotides coding for the FLAG octapeptide into the polylinker of HAVvec1 and showed that this construct was infectious and expressed the FLAG peptide. Sedimentation in sucrose gradients and Western blot analysis showed that the FLAG peptide was predominantly expressed in empty capsids fused to VP0 and forming a PreVP0 protein. Several other antigenic peptides such as the main epitope of the hepatitis B virus surface antigen and the NANP epitope of malaria have been expressed using HAVvec1. Further modifications in the constructs are being made in order to express larger polypeptides with the aim of being able to express immunuenhancers such as cytokines as part with the virus thus improving immunogenicity.